Method of making a composite with discontinuous adhesive structure

ABSTRACT

A composite includes a first substrate, a second substrate, and a discontinuous adhesive structure disposed intermediate the first and second substrates for securing the first and second substrates together to form a composite without significantly modifying the properties of either of the first and second substrates. The discontinuous adhesive structure is an array of substantially linear filaments or strands of an adhesive.

BACKGROUND OF THE INVENTION

The present invention relates to composites, and more particularly tocomposites including first and second substrates and an adhesivestructure disposed intermediate the first and second substrates forsecuring them together to form the composite.

The term "composite" as used herein and in the claims includes a firstsubstrate, a second substrate and an adhesive structure disposedintermediate the first and second substrates for securing the first andsecond substrates together. In a broader sense, the term "composite" mayinclude first and second substrates which are bound together directly(that is, without an intervening adhesive structure) but such materialsare not to be considered part of the present invention since thesubstrates useful therein are typically severely limited and thetechniques required in order to cause lamination or joinder of the firstand second substrates typically requires the property of at least one ofthe substrates to be significantly modified. Such a composite mayrequire heat, pressure or a combination thereof to be applied to thesubstrates in order to join them, as by applying one substrate in a hot,molten form to the other substrate or passing an assembly of thesubstrates through the heated nip of a pair of pressure rolls (i.e.,calendering). In such cases, the heat and/or pressure tends tosignificantly modify the properties of at least one of thesubstrates--for example, converting a breathable or vapor-permeablesubstrate into a non-breathable or vapor-impermeable substrate. Such acalendering process limits the possible substrate combinations sinceboth substrates should have a similar melting point in order to achieveadequate bonding without creating in the substrates heat-generatedpinholes which might alter the properties thereof.

In a composite, as the term is defined above--that is, requiring inaddition to the substrates an adhesive structure therebetween--there isless opportunity for one substrate to affect the other substrate sincethe adhesive structure is disposed intermediate to the two substratesand the two substrates are typically not in direct physical contact. Onthe other hand, the nature of the adhesive structure may itself affectthe properties of either substrate or the composite. Thus, theapplication of a hot melt adhesive to the substrates may cause meltingof one or both substrates (since the hot melt adhesive is typicallyapplied at temperatures of about 375° F.) or the molten adhesive mayflow into small apertures or pores of one of the substrates to render itless permeable. Even where the adhesive structure itself does notsignificantly alter the structure of the substrates directly, it may doso indirectly by modifying the properties of the composite. For example,if two breathable or water-permeable substrates are joined by acontinuous adhesive structure which is non-breathable, the adhesivestructure, in effect, negates the breathability of the substrates andresults in a non-breathable composite.

Accordingly, it is an object of the present invention to provide acomposite wherein an adhesive structure is disposed intermediate a pairof substrates for securing the substrates together to form the compositewithout significantly modifying the properties of either substratedirectly.

Another object is to provide such a composite wherein the adhesivestructure does not significantly modify the properties of either of thesubstrates indirectly--that is, it does not modify the properties of thecomposite from what they would be if the composite consisted exclusivelyof the first and second substrates.

A further object is to provide a method of forming such a composite.

It is also an object of the present invention to provide such acomposite wherein both substrates are permeable to water vapor but atleast one of the substrates is water-impermeable.

SUMMARY OF THE INVENTION

It has now been found that the above and related objects of the presentinvention are obtained in a composite, including a first substrate,second substrate, and an adhesive structure disposed intermediate thefirst and second substrates for securing them together to form thecomposite. The adhesive structure is discontinuous so that it securesthe first and second substrates together to form the composite withoutsignificantly modifying the desired properties of either of the firstand second substrates.

In a preferred embodiment, the discontinuous adhesive structurecomprises an array of substantially linear filaments or strands of anadhesive, preferably 3-100 microns in diameter. The discontinuousadhesive structure is of substantially uniform thickness and is formedof a hot melt adhesive.

In a preferred composite, the first substrate is a liquid-permeablenon-woven web, preferably a spunbond web of polyethylene orpolypropylene, about 3-40 mils in thickness. The second substrate is anon-apertured liquid-impermeable film which is microporous andvapor-permeable to, preferably a thermoplastic film with a void contentof about 25-50% and a thickness of 1-2 mils.

In other composites, the second substrate may be cellulosic tissue ormetallized film.

The composite may additionally include a third substrate, and a seconddiscontinuous adhesive structure disposed intermediate the thirdsubstrate and one of the first and second substrates for securing theone substrates and the third substrate together to form the compositewithout significantly modifying the desired properties of either of thethird substrate and the one substrate, and preferably withoutsignificantly modifying the desired properties of any of the first,second and third substrates.

Preferably, the composite is non-elastic, and the discontinuous adhesivestructure has an add-on weight of 1-23 grams per square meter.

The present invention also encompasses a method of forming a compositecomprising the steps of providing first and second substrates and thenapplying to at least one of the first and second substrates adiscontinuous adhesive structure and securing the other of the first andsecond substrates to the discontinuous adhesive structure to form acomposite, all without significantly modifying the desired properties ofeither of the first and second substrates.

In a preferred embodiment, the discontinuous adhesive structure isapplied by passing molten hot melt adhesive of suitable viscositythrough a die and, before it contacts the respective substrates, coolingthe adhesive below the temperature at which the desired properties ofthe respective substrates would be significantly modified thereby. Theadhesive structure is applied at a viscosity of 50-600 poise.Optionally, a sub-assembly formed by the first and second substrates andthe discontinuous adhesive structure therebetween is passed through apair of nip rolls to establish uniformity of contact between theadhesive structure and the substrates.

BRIEF DESCRIPTION OF THE DRAWING

The above and related objects, features and advantages of the presentinvention will be more fully understood by reference to the followingdetailed description of the presently preferred, albeit illustrative,embodiments of the present invention when taken in conjunction with theaccompanying drawing wherein:

FIG. 1 is a side elevational view of a composite according to thepresent invention; and

FIG. 2 is an isometric sectional view thereof;

FIG. 3 is a schematic view of a process for making the compositeaccording to the present invention on a generally horizontal productionline; and

FIG. 4 is a schematic view of a process for making the compositeaccording to the present invention on a generally vertical productionline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing, and in particular to FIG. 1 thereof,therein illustrated is composite according to the present invention,generally designated by the reference numeral 10. The compositecomprises a first substrate generally designated by the referencenumeral 12, a second substrate generally designated 14, and an adhesivestructure generally designated 20 and disposed intermediate the firstand second substrate 12, 14 for securing the first and second substrates12, 14 together to form the composite 10. A wide variety of differentmaterials may be employed as the first and second substrates 12, 14depending upon the final properties desired in the composite 10.Preferred composites 10 and the substrates 12, 14 used to form them willbe discussed hereinafter, it being understood that the selection of theparticular substrates is not limited to the substrates specificallytaught herein.

While the examples of the preferred composites provided below involveonly two substrates 12, 14 and an adhesive structure 20 therebetween,clearly the principles of the present invention include the use ofadditional substrates (such as a third substrate) and additionaldiscontinuous adhesive structures (such as a second discontinuousadhesive structure disposed intermediate the third substrate and one ofthe first and second substrates) for securing the one substrate and thethird substrate together to form the composite without significantlymodifying the properties of either of the one substrate and the thirdsubstrate. Indeed, the second discontinuous adhesive structure shouldnot significantly modify the properties of any of the first, second andthird substrates.

A critical feature of the present invention invention is that theadhesive structure 20 disposed intermediate the first and secondsubstrate 12, 14 for securing them together to form the composite isboth discontinuous and capable of forming the composite 10 withoutsignificantly modifying the properties of either of the first and secondsubstrates 12, 14. This is achieved by the adhesive structure 20 beingformed of an array of substantially liner filaments or strands ofadhesive. The substantial linear filaments are preferably 3-100 microns(optimally 5-30 microns) in diameter and are typically formed by passagethrough a die (for example, the die of a spinneret) so that thefilaments emerge unbroken and substantially linearly (i.e., uncrossed)from the apertures of the die. Incidental transient air currentsimpinging upon the linear filaments before they contact a substrate mayresult in some overlapping of the linear filaments as they are laid downupon the substrate; accordingly, the filaments are best described asonly being "substantially linear" rather than totally linear. Theadhesive structure 20 may be defined by continuous filaments,non-continuous filaments or a mixture of both as the continuousfilaments emerging from the die may be broken by incidental transientair currents or the like. The filaments are commonly, but notnecessarily, circular in cross section. The adhesive structure 20 is ofsubstantially uniform thickness, typically equal to the diameter of theadhesive filaments since there is essentially only a single layer offilaments intermediate the substrates 12, 14.

The discontinuous nature of the adhesive structure 20 ensures that theadhesive structure 20 will not significantly alter the properties of thesubstrates 12, 14. Thus, even if the substrates are apertured,water-permeable, or vapor-permeable, the discontinuous nature of theadhesive structure 20 permits these properties of the substrates todetermine the properties of the composite since the adhesive structureitself is discontinuous and hence grossly apertured.

The specifics of the adhesive structure 20 will vary with the intendedapplication of the composite and the properties desired therein. Thus,the adhesive useful in the present invention includestyrene-isoprene-styrene block co-polymers (SIS),styrene-ethylene-butylene-styrene block co-polymers (SEBS),styrene-butadiene-styrene co-polymers (SBS), ethylene vinylacetate (EVA)and EVA co-polymers, atactic polypropylene (APP), atacticpolyalphaolefins (APAO), VESTOPLAST (trademark of Huls America),adhesive-containing KRATON (trademark of Shell Chemical), as well asvarious combinations of the above-mentioned polymers varying inmolecular weight and plasticizer content. In selecting the mostappropriate material for the adhesive structure 20, consideration may begiven to such characteristics as bond strength, ultra-violet lightstability, gamma stability, odor, tack, and the like. The adhesives maybe pressure-sensitive or non-pressure-sensitive, as directed. Thediscontinuous adhesive structure is typically applied at an add-onweight of 1-23 grams per square meter of substrate.

Preferred hot melt adhesive includes grade 34-5533 (supplied by NationalStarch, Bridgewater, N.J.), HL-1280 or HL-6515 (supplied by H. B. FullerCompany, St. Paul, Minn.), and H-2176-01 (supplied by Findley Adhesives,Wauwatosa, Wis.). The various parameters of the process conditions willdepend, at least in part, upon the particular adhesive used. Thus, thepre-melt, main melt, transfer hose, die and air temperatures may varywith the adhesive, typical temperatures ranging from 280°-375° F. Thepre-melt temperature and main melt temperatures are the temperatures ofthe adhesive in the hot melt adhesive tank. The transfer temperature isthe temperature of the transfer hose through which adhesive is movedfrom the melt tank to the die assembly. The die temperature is thetemperature of the die assembly, and the air temperature is thetemperature of the air dispensed from the die assembly.

The adhesive strands will be prepared at a suitable rate (typically from20 to 70 grams per minute) for dispensation by air or like gas (at atemperature of about 375° F. and a flow rate of about 6-8 cfm) over an11 inch surface width of the web substrate where the web speed is100-200 feet per minute. Clearly, the adhesive output will vary with thesurface width of the web to be used and the speed of the web.

Referring now to FIG. 3, therein illustrated is a process according tothe present invention for making the composite 10 on a generallyhorizontally oriented production line. The first substrate 12 issupplied from a first substrate supply roll 32, and the second substrate14 is supplied from a second substrate supply roll 34. Both substrate12, 14 are drawn by a take-up roll 36 where the composite 10 is rolledand stored for future use. A die assembly 40 having a die 42 composed ofa plurality of tiny apertures is loaded with a quantity of the adhesiveunder pressure.

Preferably, the adhesive is a molten adhesive (e.g., a hot meltadhesive) and the die assembly 40 is heated to maintain the adhesive ata temperature which provides the appropriate viscosity for passage ofthe molten adhesive through the die apertures under the influence of airpressure (e.g., about 375° F. for a 6-8 cfm air flow). The moltenadhesive is, in effect, extruded through the die apertures in the moltenstate, but is allowed to cool before it contacts the first of thesubstrates (here illustrated as the second substrate 14) to atemperature (e.g., about 100°-125° F.) such that it does notsignificantly modify the desired properties of that first-contactedsubstrate 14. By the time the adhesive contacts the other substrate 12,it should be below the temperature at which the adhesive cansignificantly modify the desired properties of that other substrate 12.Where the adhesive is brought into contact with both substrates 12, 14substantially simultaneously, then the adhesive must be cooled before itcontacts either substrate, to a temperature at which it will notsignificantly modify the properties of either substrate 12, 14.Preferably the adhesive structure is allowed to cool so that it has aviscosity of about 50-600 poise immediately prior to contacting thefirst substrate.

The adhesive filaments or strands emitted from the die apertures arepreferably allowed to cool naturally (i.e., through heat dissipation toambient or warm air over the time required for the filaments to reachthe substrates) although positive cooling of the filaments may beeffected, for example, by an impinging stream of relatively cool air.Any positive cooling of the filaments should be conducted atsufficiently low air velocities that the filaments remain substantiallylinear with only minimal overlapping and crossing. In order to providesufficient time for natural or unassisted cooling, the distance betweenthe die head and the web (known as the "die assembly height") ispreferably about 1.5-6.0 inches, and optimally about 2.25 inches, sothat the adhesive has an opportunity to naturally cool sufficientlybefore it strikes the web. A lesser spacing may be adequate wherepositive cooling is used.

The adhesive is typically applied to the web at an angle of about 90°,although this angle may be varied as desired for particularapplications. The resultant fabric bond area (i.e., the percentage ofthe area of each substrate covered by the adhesive) may varysubstantially and is preferably from about 4 to 21%.

The adhesive used for the adhesive structure 20 has sufficient tackthat, at least with applied pressure, it will bond adequately with thetwo substrates 12, 14. Preferably, but not necessarily, the sub-assemblyformed by the first and second substrates 12, 14 and the discontinuousadhesive structure 20 therebetween is passed through a pair of unheatednip rolls 48 (e.g., the nip rolls of a cooled calendar) to establishuniformity of contact between the adhesive structure 20 and thesubstrates 12, 14, as illustrated in FIG. 3. The nip rolls may berubber-coated, coarse or smooth plasma-coated, Teflon-coated or the likeand may be cooled by circulating water or refrigerant. In order toassist adequate cooling of the adhesive structure 20 before passagethrough the cool nip rolls 48, the separation or distance from the die(actually the point on the web which first receives the adhesive) to thenip along the length of the sub-assembly is preferably about 26 inchesfor a web speed of 100-200 feet per minute, the die-to-nip distanceincreasing with increasing web speed.

It will be appreciated that the application of the adhesive structure tothe substrates 12, 14 described above does not significantly modify thedesired properties of the substrates 12, 14. By way of contrast,application of an adhesive through conventional rotogravure techniquestends to produce sheets or relatively large globs of adhesive, whileapplication of an adhesive through conventional blowing of the adhesiveonto a substrate tends to produce wide variations in the thickness ofthe adhesive structure produced. In contrast, the method of the presentinvention enables the adhesive structure 20 to be formed with variationsof thickness across the width of the substrates of as little as plus orminus 2%. Accordingly, the present invention provides a thin and uniformadhesive structure, typically about as thick as the adhesive filamentdiameter. Since the adhesive structure 20 is at a temperature of onlyabout 100°-125° F. at the time of contact with the substrate, any of awide variety of substrates may be used to form a composite according tothe present invention. Where the porous or permeable structure of asubstrate is to be maintained, the substrate need only have a meltingpoint higher than that of the adhesive structure contacting the same(namely, typically about 100°-125° F.).

Referring now to FIG. 4, therein illustrated is another production linefor the manufacture of the composite 10 according to the presentinvention, this production line differing from the production line ofFIG. 3 because it is vertically oriented rather than horizontallyoriented. Elements of the production line having the same structure andfunction as the production line of FIG. 3 are similarly numbered.

In the vertically oriented production line, the adhesive emitted fromthe die 42 of the die assembly 40 preferably contacts both substrates12, 14 at the same time so that the application of the adhesivestructure 20 to at least one of the substrates 12, 14 and the securingof the other substrate to the adhesive structure 20 occurssimultaneously. The adhesive preferably contacts the substrates 12, 14as they enter the nip of the rolls 48. Typically the angle at which theadhesive is applied to the substrates 12, 14 is less than 90° and may bedifferent for its contact with each of the substrates 12, 14.

In such a production line, the supply rolls 32, 34 for the substrates12, 14, respectively, as well as the die assembly 40 and die 42, aredisposed above the plane of the rolls 48 while the take-up roll 36 istypically disposed below the plane of the rolls 48, as illustrated inFIG. 4. However, the actual location of the supply rolls 32, 34 and thetake-up roll 36 may be varied and, if desired, may be on opposite sidesof the plane of the rolls 48. Similarly, while the adhesive isillustrated in FIG. 4 as contacting both substrates 12, 14simultaneously, when desired, the die 42 may be shifted to one side orthe other so that the adhesive emitted therefrom contacts one of thesubstrates 12, 14 before the other.

A first embodiment of the composite 10 has fluid barrier propertiesuseful in medical and industrial protective garments such as surgicalgowns, disposable protective garments, etc. The composite 10 employs aliquid-permeable non-woven web as the first substrate 12 (typically asthe inner or wearer-facing surface), a breathable or vapor-permeable,non-liquid permeable film as the second substrate 14 (typically as theouter or exposed surface), and a hot melt adhesive as the adhesivestructure 20 joining the two substrates 12, 14.

More particularly, the first substrate 12 is preferably a spunbondedpolyethylene web having a 3-40 mils thickness corresponding to a basicweight of about 0.3-3.5 oz./sq. yard (osy), and optimally 1.0 oz./sq.yard. Preferred non-woven webs 12 of the composite 10 are spunbonded,carded, spun-laced, melt-blown or the like. The web 12 may be treated todissipate static charges as necessary for anti-static propertiesdesirable in protective clothing. A chemical finish may be applied tothe web surface in order to repel specific fluids. The spunbonded webmay have an embossed area covering, for example, 14% of the surface ofthe web. A fiber denier of 3-6 is preferred because it offers highstrength and flexibility. While the resultant web typically feels soft,pliable and comfortable, the textile-like feel or hand may be enhancedby the use of spun-laced non-wovens. Alternatively, the first substrate12 is preferably a spunbonded polypropylene web having a basis weight of1.5 osy.

The second substrate 14 is preferably a microporous thermoplastic filmhaving a 1.0 mil thickness. Preferred films 14 of the composite 10 areeither a linear, low-density polyethylene or a polypropylene-based film.The pore or void content in the breathable film is preferably 25-50%,with a preferred void content of about 40%, although other void contentsmay be useful for specific applications. The pore size and content canbe varied depending upon the amount of moisture vapor transmissiondesired through the film. For a pore content of 25-50% and a pore sizenot in excess of 15 microns, moisture vapor transmission rates of5,000-11,000 g/m² /24 hours (at 100° F., 100% relative humidity) areobtainable. Where protection against a virus is desired, this film canbe doubled over, if necessary, to form a viral barrier. Corona chargingof the film may be used to modify its surface tension, either to improveits adhesion properties or its fluid repellent properties. Additionally,such corona charging enhances printability of the structure whereprinting of designs and logos on the composite is desired. The film 14may also be one of the commercially available products permeable towater vapor but impermeable to liquid water (e.g., a polyethylenemicroporous product available under the trade name EXXAIRE from Exxon).

The filamentary hot melt adhesive layer 20 may be sprayed directly ontothe spunbonded web 12 using any one of the commercially availablesystems for continuous spraying of a uniform layer of hot melt adhesive(such as those available from Mercer Corporation of Hendersonville,Tenn. and Acumeter Laboratories, Inc. of Marlborough, Md.).

In the composite 10 thus formed, the spunbonded layer 12 providesstrength and dimensional stability as well as softness (hand) and othertextile-like properties. The adhesive structure 20 adheres substrates12, 14 together, the small adhesive filament or strand diameter and itsuniform distribution preventing the overall composite from becomingstiff, losing its textile-like hand, or having an uneven thickness.While the spunbonded web 12 is permeable to both liquid water and watervapor, the film substrate 14 is impermeable to liquid water and preventsstrikethrough of potentially harmful liquids while still enabling thetransmission of water vapor (e.g., sweat) through a garment made thereofto enhance user comfort.

In a related composite 10, the breathable, vapor-permeable filmsubstrate 14 is replaced with a non-breathable, vapor-impermeable filmsubstrate. This composite provides a total barrier construction and istherefore useful in garments to be used in extremely hazardousapplications (such as asbestos removal or to prevent strikethrough ofblood contaminated with liquid-borne pathogens), albeit with somereduction in user comfort since wearer sweat cannot evaporatetherethrough. The total barrier laminate can be used for construction ofeither the entire garment or merely discretely placed zones of thegarment (e.g., forearms and chest).

In still other composites 10, the breathability or barrier properties ofthe composite may be of no concern, the advantages of the compositearising out of one or more of its other properties--e.g., softness(hand), strength, dimensional stability, absorptiveness, etc.

EXAMPLES Example 1

Film: EXXAIRE, a linear low density polyethylene biaxially orientedmicroporous membrane (supplied by Exxon Chemical, Buffalo Grove, Ill.)having a thickness of about 1.0 mil, a surface tension of about 35dynes/cm, a pore size which does not typically exceed 12 microns, and areported moisture vapor transmission rate of 6,000-10,000 g/m² /24hours.

Web: A non-woven spunbonded polypropylene web, thermally bonded, havingan embossed area of approximately 14 per cent over the surface of theweb, and a fiber denier of 3-6.

Using the equipment shown in FIG. 1, the film and web substrates werebonded together using hot melt adhesive grade 34-5533 (supplied byNational Starch, Bridgewater, N.Y.). Other process conditions were asset forth in Table I below.

The resultant composite structure was soft yet strong, and had very goodmoisture barrier properties suitable for industrial and medicalapplications.

Example 2

Film: EXXAIRE

Web: A non-woven polyester web SONTARA (supplied by Dupont, Wilmington,Del.).

Using the equipment shown in FIG. 1, the film and web substrates werebonded together using hot melt adhesive HL-1280 (supplied by H. B.Fuller Company, St. Paul, Minn.). The hydroentangled web weight wasapproximately 1.2 osy and had a polyester fiber blend. Other processconditions were as set forth in Table I below.

The resultant composite structure had a soft hand yet possessed goodphysical characteristics, including very good barrier propertiessuitable for industrial and medical applications and comparable to thoseof the film by itself.

Example 3

Film: EXXAIRE

Web: A non-woven spunbonded polyethylene web thermally bonded, weighingabout 1.0 osy, having a point bonded area of approximately 14 per centover the surface of the web, and a fiber denier of 3-6 denier.

Using the equipment shown in FIG. 1 the film and web substrates werebonded together using the hot melt adhesive of Example 2. Other processconditions were as set forth in Table I below.

The resultant composite structure had a soft hand and excellent moisturebarrier properties comparable to those of the film by itself.

Example 4

Film: A metallized biaxially oriented polypropylene film (supplied byQuantum Performance Films, Streamwood, Ill.).

Web: A non-woven spunbonded polypropylene web weighing 1.25 osy,thermally bonded, having an embossed area of approximately 14 per centover the surface of the web, and a fiber denier of 3-6 denier.

Using the equipment shown in FIG. 1, the film and web substrates werebonded together using hot melt adhesive HL-6515 (supplied by H. B FullerCompany, St. Paul Minn.). Other process conditions were as set forth inTable I below.

The resultant composite structure possessed excellent moisture barrierand softness properties.

Example 5

Web A: The non-woven airlaid web used was a 32 lbs. cellulosic tissue(supplied by Fort Howard, Wis.).

Film: An embossed polyethylene film (supplied by Rochelle Plastics,Rochelle, Ill.)

Web B: A wetlaid non-woven textile grade 3557D (supplied by DexterNonwovens, Windsor Locks, Conn.).

Using the equipment shown in FIG. 1, the film and web A substrates werebonded together using hot melt adhesive H-2176-01 (supplied by FindleyAdhesives, Wauwatosa, Wis.). Other process conditions were as set fourthin Table I below.

The resultant composite structure was subsequently bonded to web B underthe same process conditions so that the film was between the tissue andwetlaid non-woven layers. The resultant material had properties usefulin medical applications. The cellulosic tissue layer (web A) provided ahigh level of absorption of bodily fluids, the film layer provided agood moisture barrier, and the wetlaid textile layer (web B) provided adesirable strength and softness.

                  TABLE I                                                         ______________________________________                                                       Example Number                                                                1    2       3      4    5                                     ______________________________________                                        Process Conditions                                                            Pre-Melt T, °F.                                                                         300    280     297  330  350                                 Main Melt T, °F.                                                                        300    280     295  330  350                                 Hose T, °F.                                                                             300    300     301  330  350                                 Die T, °F.                                                                              300    300     300  331  350                                 Air T, °F.                                                                              375    375     375  375  375                                 Air Flow Rate, cfm                                                                              8      8       8    8    6                                  Adhesive Output, gpm*                                                                           59      24.5   24   64   27                                 Web Speed, fpm   200    100     100  200  100                                 ______________________________________                                                        Ex. 2   Ex. 3                                                 ______________________________________                                        Comparative Test Results                                                      MVTR, g/m.sup.2 /24/Hrs.                                                      Film              7,000-8,000                                                                             7,000-8,000                                       Composite         7,600     6,500                                             Gurley Porosity, sec/100 cc                                                   Film              300-400   300-400                                           Composite         250       200-300                                           ______________________________________                                         *Applied over an 11 inch width of web substrate at an adhesive applicatio     angle of 90°, with a die assembly height of 2.25 inches and a          dieto-nip distance of 26 inches.                                         

The comparative results for porosity of the film vis-a-vis the compositefor Examples 2 and 3 clearly show that the porosity of the composite wassubstantially equal to that of the film alone.

The test methods used in the examples were as follows:

Water or Moisture Vapor Transmission Rate (WVTR or MVTR) Through PlasticFilm and Sheeting: ASTM F 1249-90 Using a Modulated Infrared Sensor.

Gurley Porosity: ASTM D726, Method A

Hydrostatic Pressure Test: American Association of Colorists andChemists Test Method 127-1985

Thickness: ASTM D1777

Weight: ASTM D1910

To summarize, the present invention provides a composite wherein anadhesive structure is disposed intermediate a pair of substrates tosecure the substrates together to form the composite withoutsignificantly modifying the properties of either substrate eitherdirectly or indirectly (that is, by modifying the properties of thecomposite from what they would be if the composite consisted exclusivelyof the first and second substrates). The present invention provides amethod of forming such a composite. In a preferred embodiment of thecomposite both substrates are permeable to water vapor, but at least oneof the substrates is water-impermeable.

Now that the preferred embodiments of the present invention have beenshown and described in detail, various modifications and improvementsthereon will readily become apparent to those skilled in the art.Accordingly, the spirit and scope of the present invention is to beconstrued broadly and limited only by the appended claims, and not bythe foregoing specification.

We claim:
 1. A method of forming a composite comprising the steps of:(A)providing first and second substrates; (B) applying to at least one ofthe first and second substrates an adhesive structure which isdiscontinuous across the width of the one substrate, the adhesivestructure comprising an array of substantially linear, primarilyunbroken and elongated filaments of adhesive of a substantially uniformdiameter, said diameter being about 3 to 100 microns, the adhesivestructure having a thickness which does not vary more than plus or minus2%, and securing the other of the first and second substrates to theadhesive structure to form a composite, all without significantlymodifying the desired properties of either of the first and secondsubstrates.
 2. The method of claim 1 wherein the discontinuous adhesivestructure is applied by passing molten hot melt adhesive of suitableviscosity through a die and, before it contacts the respectivesubstrates, cooling the adhesive below the temperature at which thedesired properties of the respective substrates would be significantlymodified thereby.
 3. The method of claim 2 wherein said adhesive iscooled by allowing the adhesive to cool after it passes through the dieand before it contacts the respective substrates, without positivecooling thereof.
 4. The method of claim 1 wherein the adhesive structureis applied at a viscosity of 50-600 poise and covers about 4 to 21% ofeach of the first and second substrates.
 5. The method of claim 1wherein a sub-assembly formed by the first and second substrates and thediscontinuous adhesive structure therebetween is passed through a pairof cooled nip rolls to cool and establish uniformity of contact betweenthe adhesive structure and the substrates.
 6. The method of claim 1,wherein at least one of the first and second substrates is polyethylene.7. The method of claim 1 wherein the adhesive structure covers about 4to 21% of the first and second substrates.
 8. The method of claim 1including the step of applying a gas stream to the filaments of thediscontinuous adhesive structure prior to application of the filamentsto either substrate, the gas stream being at an angle of 90° to thefilaments and at a temperature greater than that of the filaments. 9.The method of claim 1 wherein the composite once formed, is immediatelypassed through cooled nip rolls.
 10. A method of forming a compositecomprising the steps of:(A) providing first and second substrates; (B)applying to at least one of the first and second substrates at aviscosity of 50-600 poise an adhesive structure which is discontinuousacross the width of the one substrate, comprising an array ofsubstantially linear, primarily unbroken and elongated filaments ofadhesive of a substantially uniform diameter, said diameter being about3 to 100 microns, the adhesive structure being about as thick as thediameter of the filaments, by passing molten hot melt adhesive through adie and, before it contacts the respective substrates, allowing theadhesive to cool below the temperature at which the desired propertiesof the respective substrates would be significantly modified thereby andsubjecting the adhesive structure to a gas stream hotter than theadhesive structure and transverse to its axis of motion, and thensecuring the other of the first and second substrates to the adhesivestructure to form a composite and passing the composite through coolednip rolls, all without significantly modifying the desired properties ofeither of the first and second substrates.
 11. A method of forming acomposite comprising the steps of:(A) providing first and secondsubstrates; (B) applying to at least one of the first and secondsubstrates at a viscosity of 50-600 poises an adhesive structure whichis discontinuous across the width of the one substrate, the adhesivestructure comprising an array of substantially linear, primarilyunbroken and elongated filaments of hot melt adhesive of a substantiallyuniform diameter, said diameter being about 3 to 100 microns, saidfilaments being substantially parallel to one another at any point alongthe width of the substrates, and said adhesive structure covering about4 to 21% of each of the first and second substrates and having athickness about the same as the diameter of said filaments, by passingmolten hot melt adhesive through a die and, before it contacts therespective substrates, allowing the adhesive to cool below thetemperature at which the desired properties of the respective substrateswould be significantly modified thereby and subjecting the adhesivestructure to a gas stream hotter than the adhesive structure andtransverse to its axis of motion, and then securing the other of thefirst and second substrates to the adhesive structure to form acomposite and passing the composite through cooled nip rolls, allwithout significantly modifying the desired properties of either of thefirst and second substrates.